1. Field of the Invention
The present invention relates to an addition-curable type curable silicone resin composition.
2. Description of the Related Art
Lenses for light-emitting diode (LED) devices are mass manufactured by mechanical molding such as injection molding. As a lens material for LED, a material having high transparency, high refractive index, having excellent mechanical characteristics, heat resistance, and light resistance has been required. For such a use, an epoxy resin, a poly(meth)acrylate resin and a polycarbonate resin have been conventionally used in many cases, but the currently increasing an output of LED light-emitting devices and the circumstances at high temperatures for a long period of time cause the problem that the thermoplastic resins are insufficient in heat resistance and discoloration resistance.
In addition, lead-free solders are often used in recent years. The lead-free solders have a higher melting point than those of the conventional solders, so that optical devices are usually soldered to substrates while heating at a temperature of 260° C. or higher. When soldering is carried out such a temperature, lenses of prior art thermoplastic resins can no longer be used because inconveniences occur that the lenses will deform or yellow due to high temperature.
Under such a circumstance, a number of studies have been made on the use of silicone resins which are so-called MQ resin comprising an M unit and a Q unit in the lenses associated with LED whereby manufacturing lenses excellent in heat resistance (Patent Documents 1 to 3).
However, the cured product molded by using the silicone resin is hard and weak in cold/heat shock, so that there is a problem that cracks occur due to internal stress by sudden temperature change. To overcome the brittleness of the MQ resin, a vinyl resin into which a T unit such as PhSiO3/2 has been introduced and an MQ resin having a SiH group have been used. When the T unit is used, brittleness can be overcome but there are defects that the product is inferior in heat resistance, and colored by heating for a long period of time (Patent Document 4).
Also, there is an example using a silicone resin comprising an M unit, a D unit and a Q unit to improve workability and rubber physical property (Patent Document 5), but there is no resin which satisfies all of high transparency, high refractive index, excellent mechanical properties, heat resistance and light resistance.